Coating for decorative metals with improved mar and scratch resistance and methods of application

ABSTRACT

Coated articles comprising a decorative metal substrate and a transparent cured coating thereon containing inorganic particles in which the concentration of particles in the exposed surface region of the cured coating is greater than the bulk region of the coating. Preferably, the transparent coating is applied by electrodeposition.

FIELD OF THE INVENTION

The present invention relates to coated articles, particularlydecorative articles, and to methods for coating the articles byelectrodeposition such that the articles have improved mar and scratchresistance.

BACKGROUND OF THE INVENTION

Decorative metals, such as brass, bronze, polished steel and aluminum,and articles derived therefrom, such as hardware and jewelry, aluminumand steel trim parts, are often coated with a clear or tintedtransparent coating to enhance the durability and weatherability of thearticle. A disadvantage of many of these protective coatings is thatthey have poor mar and scratch resistance.

The present invention provides a coated decorative metal substrate withimproved mar and scratch resistance and applying by electrodeposition acoating that provides improved mar and scratch resistance.

SUMMARY OF THE INVENTION

The present invention provides a coated article comprising:

-   -   (a) a decorative substrate,    -   (b) a transparent coating thereon containing inorganic particles        in which the concentration of particles in the exposed surface        region of the coating is greater than the concentration of the        particles in the bulk regions of the coating.

The invention also provides a method of forming an abrasion-resistantcoating on an electroconductive substrate comprising:

-   -   (a) electrodepositing onto the substrate a curable        electrodepositable composition comprising:        -   (i) a curable resinous binder,        -   (ii) inorganic particles,        -   (iii) a surface active agent;    -   (b) curing the composition to form a substantially continuous        coating on the substrate with a surface exposed to the        atmosphere while the inorganic particles migrate to the exposed        surface region of the coating.

DETAILED DESCRIPTION OF THE DRAWINGS

The drawing is a transmission electron photomicrograph 13,000×magnification of a cross-section of a cured electrodeposited coating ofExample 1, infra.

DETAILED DESCRIPTION

The decorative substrates of the invention have a bright shinyappearance as measured by their specular reflectance. The specularreflectance can be determined by measuring the specular gloss inaccordance with ASTM D2457, D523 using a BYK GARDNER, RIMHAZE-GLOSSMETER. Accordingly, when the specular gloss is determined bythis method at a 60° incident angle (60° specular gloss), the glossreadings are greater than 100, typically greater than 200, often greaterthan 300 and greater than 400. Preferably, the decorative substrates areelectroconductive and are metals. Examples of such decorative metals arepolished steel and aluminum, copper, polished bronze, brass, preciousmetals such as gold and silver, and substrates that have been plated orcoated to give a bright shiny metal appearance such as chrome platedsteel or nickel plated steel and copper plated substrates.

The decorative metals find use in applications such as bright hardware,for example, brass doorknobs, mail receptacles, precious metal jewelry,aluminum and steel trim parts for automotive applications.

As mentioned above, the decorative substrates are preferably electroconductive which permits the application of the protective coating byelectrodeposition. However, the protective coating can be applied bymore conventional techniques such as spraying, immersion coating androil coating. In the latter case, the substrate need not beelectroconductive.

The coating composition that is applied to the decorative metalcomprises a curable resinous binder, inorganic particles and a surfaceactive agent. The resinous binder contains a film-forming resin havingreactive functional groups and a curing agent having functional groupsthat are reactive with the functional groups of the film-forming resin.The film-forming resin and curing agent can be contained in one resinousbinder that has different coreactive functional groups. For example, aresinous binder containing hydroxyl groups and blocked isocyanategroups.

The film-forming resin is preferably ionic such that the curableresinous composition can be applied by electrodeposition. The resin canbe anionic or cationic and is preferably cationic in nature.

Examples of film-forming resins suitable for use in anionicelectrodepositable coating compositions are base-solubilized, carboxylicacid containing polymers such as the reaction product or adduct of adrying oil or semi-drying fatty acid ester with a dicarboxylic acid oranhydride; and the reaction product of a fatty acid ester, unsaturatedacid or anhydride and any additional unsaturated modifying materialswhich are further reacted with polyol. Also suitable are the at leastpartially neutralized interpolymers of hydroxy-alkyl esters ofunsaturated carboxylic acids such as hydroxyethyl acrylate and/orhydroxymethyl methacrylate, unsaturated carboxylic acids such as acrylicor methacrylic acid, and at least one other ethylenically unsaturatedmonomer such as lower alkyl esters of acrylic and methacrylic acid, forexample, ethyl acrylate and butyl methacrylate. Such interpolymers orresins are commonly referred to as (meth)acrylic resins. Still anothersuitable electrodepositable resin comprises an alkyd-aminoplast vehicle,i.e., a vehicle containing an alkyd resin and an amine-aldehyde resin.Yet another anionic electrodepositable resin composition comprises mixedesters of a resinous polyol. These compositions are described in detailin U.S. Pat. No. 3,749,657 at col, 9, lines 1 to 75 and col, 10, lines 1to 13, all of which are herein incorporated by reference. Other acidfunctional polymers can also be used such as phosphatized polyepoxide orphosphatized acrylic polymers as are well known to those skilled in theart.

As aforementioned, it is preferred that the ionic electrodepositableresin (a) is capable of deposition on a cathode. Examples of suchcationic film-forming resins include amine salt group-containing resinssuch as the acid-solubilized reaction products of polyepoxides andprimary or secondary amines such as those described in U.S. Pat. Nos.3,663,389; 3,984,299; 3,947,338; and 3,947,339. Usually, these aminesalt group-containing resins are used in combination with a blockedisocyanate curing agent. The isocyanate can be fully blocked asdescribed in the aforementioned U.S. Pat. No. 3,984,299 or theisocyanate can be partially blocked and reacted with the resin backbonesuch as described in U.S. Pat. No. 3,947,338. Also, one-componentcompositions as described in U.S. Pat. No. 4,134,866 and DE-OS No.2,707,405 can be used as the film-forming resin. Besides the epoxy-aminereaction products, film-forming resins can also be selected fromcationic acrylic resins such as those described in U.S. Pat. Nos.3,455,806 and 3,928,157. Besides cationic amine salt group containingresins, sulfonium salt group containing resins can also be used.Examples of such resins are sulfonium group containing (meth)acrylicresins as disclosed in U.S. Pat. No. 4,038,232.

Examples of suitable curing agents are aminoplasts that are reactivewith hydroxyl groups and carboxylic acid groups associated with afilm-forming resin and are the preferred curing agent for anionicfilm-forming resins. Other curing agents are polyisocyanates that arereactive with hydroxyl groups and primary and secondary amine groupsassociated with the film-forming resin and are preferably curing agentsfor cationic film-forming resins.

Aminoplast resins are well known in the art. Aminoplasts can be obtainedfrom the condensation reaction of formaldehyde with an amine or amide.Nonlimiting examples of amines or amides include melamine, urea, orbenzoguanamine. While the aldehyde used is most often formaldehyde,other aldehydes such as acetaldehyde, crotonaldehyde, and benzaldehydecan be used.

The aminoplast contains imino and methylol groups and in certaininstances at least a portion of the methylol groups are etherified withan alcohol to modify the cure response. Any monohydric alcohol can beemployed for this purpose including methanol, ethanol, n-butyl alcohol,isobutanol, and hexanol.

Nonlimiting examples of aminoplasts include melamine-, urea-, orbenzoguanamine-formaldehyde condensates, in certain instances monomericand at least partially etherified with one or more alcohols containingfrom one to four carbon atoms. Nonlimiting examples of suitableaminoplast resins are commercially available, for example from CytecIndustries, Inc. under the trademark CYMEL®, and from Solutia, Inc.under the trademark RESIMENE®.

Other curing agents suitable for use include, but are not limited to,polyisocyanate curing agents. As used herein, the term “polyisocyanate”is intended to include blocked (or capped) polyisocyanates as well asunblocked polyisocyanates. The polyisocyanate can be an aliphatic or anaromatic polyisocyanate, or a mixture of the foregoing two.Diisocyanates can be used, although higher polyisocyanates such asisocyanurates of diisocyanates are often used. Higher polyisocyanatesalso can be used in combination with diisocyanates. Isocyanateprepolymers, for example reaction products of polyisocyanates withpolyols also can be used. Mixtures of polyisocyanate curing agents canbe used.

If the polyisocyanate is blocked or capped, any suitable aliphatic,cycloaliphatic, or aromatic alkyl monoalcohol known to those skilled inthe art can be used as a capping agent for the polyisocyanate. Othersuitable capping agents include oximes and lactams.

The particles suitable for use in the coating compositions of theinvention can comprise inorganic elements or compounds known in the art.Suitable particles can be formed from ceramic materials, metallicmaterials, and mixtures of any of the foregoing. Suitable ceramicmaterials comprise metal oxides, metal nitrides, metal carbides, metalsulfides, metal silicates, metal borides, metal carbonates, and mixturesof any of the foregoing. Specific, nonlimiting examples of metalnitrides are, for example boron nitride; specific, nonlimiting examplesof metal oxides are, for example zinc oxide; nonlimiting examples ofsuitable metal sulfides are, for example molybdenum disulfide, tantalumdisulfide, tungsten disulfide, and zinc sulfide; nonlimiting suitableexamples of metal silicates are, for example aluminum silicates andmagnesium silicates such as vermiculite.

The particles can comprise, for example a core of essentially a singleinorganic oxide such as silica in colloidal, fumed, or amorphous form,alumina or colloidal alumina, titanium dioxide, cesium oxide, yttriumoxide, colloidal yttria, zirconia, e.g., colloidal or amorphouszirconia, and mixtures of any of the foregoing; or an inorganic oxide ofone type upon which is deposited an organic oxide of another type. Sincethe cured composition of the invention is employed as a transparentcoating, the inorganic particles should not seriously interfere with theoptical properties of the cured composition. As used herein,“transparent” means that the cured coating has a BYK Haze index of lessthan 50, more typically less than 25, as measured using a BYK/Haze Glossinstrument.

Preferably, the inorganic particles are colloidal silica particles insitu by a sol-gel process in which alkoxy silanes are hydrolyzed inalcohol/water mixture to form colloidal silica particles in situ.

The inorganic particles have an average particle size of less than 1000nanometers, typically from 1 to 100, and from 1 to 50 nanometers, andoften from 5 to 25 nanometers.

The average particle size can be determined by visually examining anelectron micrograph of a transmission electron microscopy (“TEM”) image,measuring the diameter of the particles in the image, and calculatingthe average particle size based on the magnification of the TEM image.For example, a TEM image with 105,000× magnification is produced, and aconversion factor is obtained by dividing the magnification by 1000.Upon visual inspection, the diameter of the particles is measured inmillimeters, and the measurement is converted to nanometers using theconversion factor. The diameter of the particle refers to the smallestdiameter sphere that will completely enclose the particle.

The shape (or morphology) of the particles can vary depending upon thespecific embodiment of the present invention and its intendedapplication. For example generally spherical morphologies (such as solidbeads, microbeads, or hollow spheres), can be used, as well as particlesthat are cubic, platy, or acicular (elongated or fibrous).

The inorganic particles have a Mohs' hardness value greater than 5, moretypically greater than 6.

Also present in the coating composition is a surface active agent thatcan be present as a separate component or can be prereacted with theinorganic particles.

The surface active agent can be selected from anionic, nonionic, andcationic surface active agents.

As used herein, by “surface active agent” is meant any material thattends to lower the solid surface tension or surface energy of the curedcomposition or coating. That is, the cured composition or coating formedfrom a composition comprising a surface active agent has a lower solidsurface tension or surface energy than a cured coating formed from theanalogous composition which does not contain the surface active agent.

Nonlimiting examples of suitable anionic surface active agents includesulfates or sulfonates. Specific nonlimiting examples include higheralkyl mononuclear aromatic sulfonates such as the higher alkyl benzenesulfonates containing from 10 to 16 carbon atoms in the alkyl group anda straight- or branched-chain, e.g., the sodium salts of decyl, undecyl,dodecyl, tridecyl, tetradecyl, pentadecyl or hexadecyl benzene sulfonateand the higher alkyl toluene, xylene and phenol sulfonates; alkylnaphthalene sulfonate, and sodium dinonyl naphthalene sulfonate.

Nonlimiting examples of nonionic surface active agents suitable for usein the cured composition or coating of the present invention includethose containing ether linkages and which are represented by thefollowing general formula: RO(R′O)_(n)H; wherein the substituent group Rrepresents a hydrocarbon group containing 6 to 60 carbon atoms, thesubstituent group R′ represents an alkylene group containing 2 or 3carbon atoms, and mixtures of any of the foregoing, and n is an integerranging from 2 to 100, inclusive of the recited values.

Such nonionic surface active agents can be prepared by treating fattyalcohols or alkyl-substituted phenols with an excess of ethylene orpropylene oxide. The alkyl carbon chain may contain from 14 to 40 carbonatoms and may be derived from a long chain fatty alcohol such as oleylalcohol or stearyl alcohol. Nonionic polyoxyethylene surface activeagents of the type represented by the formula above are commerciallyavailable under the general trade designation SURFYNOL from Air ProductsChemicals, Inc.; PLURONIC or TETRONIC from BASF Corporation; TERGITOLfrom Union Carbide; and SURFONIC from Huntsman Corporation.

As indicated above, cationic surface active agents also can be used.Nonlimiting examples of cationic surface active agents suitable for usein the cured compositions or coatings of the present invention includeacid salts of alkyl amines such as ARMAC HT, an acetic acid salt ofn-alkyl amine available from Akzo Nobel Chemicals; imidazolinederivatives such as CALGENE C-100 available from Calgene Chemicals Inc.;ethoxylated amines or amides such as DETHOX Amine C-5, a cocoamineethoxylate available from Deforest Enterprises ethoxylated fatty aminessuch as ETHOX TAM available from Ethox Chemicals, Inc.; and glycerylesters such as LEXEMUL AR, a glyceryl stearate/stearaidoethyldiethylamine available from Index Chemical Co.

When the coating compositions contain anionic film-forming resins,anionic or non-ionic surface active agents should be used. When thecoating compositions contain cationic film-forming resins, cationic ornon-ionic surface active agents should be used.

Preferably, the surface active agent is selected from at least onepolysiloxane comprising at least one reactive functional group, the atleast one polysiloxane comprising at least one of the followingstructural units (I):

R¹ _(n)R² _(m)SiO_((4-n-m)/2)  (I)

wherein each R¹, which may be identical or different, represents H, OH,a monovalent hydrocarbon group or a monovalent siloxane group; each R²,which may be identical or different, represents a group comprising atleast one reactive functional group, wherein m and n fulfill therequirements of 0<n<4, 0<m<4 and 2≦(m+n)<4.

It should be understood that the “at least one polysiloxane having atleast one structural unit (I)” above is a polymer that contains at leasttwo Si atoms per molecule. As set forth above, the term “polymer” inmeant to encompass oligomers, and includes without limitation bothhomopolymers and copolymers. It should also be understood that the atleast one polysiloxane can include linear, branched, dendritic or cyclicpolysiloxanes.

Also, as used herein, the term “reactive” refers to a functional groupthat forms a covalent bond with another functional group underconditions sufficient to cure the composition.

Each of m and n depicted in the at least one structural unit (I) abovefulfill the requirements of 0<n<4, 0<m<4 and 2≦(m+n)<4. When (m+n) is 3,the value represented by n can be 2 and the value represented by m is 1.Likewise, when (m+n) is 2, the value represented by each of n and m is1.

As used herein, a “monovalent hydrocarbon group” means a monovalentgroup having a backbone repeat unit based exclusively on carbon. As usedherein, “monovalent” refers to a substituent group that, as asubstituent group, forms only one single, covalent bond. For example amonovalent group on the at least one polysiloxane will form one singlecovalent bond to a silicon atom in the backbone of the at least onepolysiloxane polymer. As used herein, “hydrocarbon groups” are intendedto encompass both branched or unbranched hydrocarbon groups.

Thus, when referring to a “monovalent hydrocarbon group,” thehydrocarbon group can be branched or unbranched, acyclic or cyclic,saturated or unsaturated, or aromatic, and can contain from 1 to 24 (orin the case of an aromatic group from 3 to 24) carbon atoms. Nonlimitingexamples of such hydrocarbon groups include alkyl, alkoxy, aryl,alkaryl, and alkoxyaryl groups. Nonlimiting examples of lower alkylgroups include, for example methyl, ethyl, propyl, and butyl groups. Asused herein, “lower alkyl” refers to alkyl groups having from 1 to 6carbon atoms. One or more of the hydrogen atoms of the hydrocarbon canbe substituted with heteroatoms. As used herein, “heteroatoms” meanselements other than carbon, for example oxygen, nitrogen, and halogenatoms.

As used herein, “siloxane” means a group comprising a backbonecomprising two or more —SiO— groups. For example, the siloxane groupsrepresented by R¹, which is discussed above, and R, which is discussedbelow, can be branched or unbranched, and linear or cyclic. The siloxanegroups can be substituted with pendant organic substituent groups, forexample alkyl, aryl, and alkaryl groups. The organic substituent groupscan be substituted with heteroatoms, for example oxygen, nitrogen, andhalogen atoms, reactive functional groups, for example those reactivefunctional groups discussed above with reference to R², and mixtures ofany of the foregoing.

In another embodiment, each substituent group R², which may be identicalor different, represents a group comprising at least one reactivefunctional group such as a hydroxyl group or a carboxyl group.

In one embodiment, the present invention is directed to a curedcomposition as previously described, wherein the at least onepolysiloxane comprises at least two reactive functional groups such ashydroxyl groups. The at least one polysiloxane can have a reactive groupequivalent weight ranging from 50 to 1000 mg, preferably 100 to 500 mgper gram of the at least one polysiloxane.

In one embodiment, the present invention is directed to a curedcomposition as previously described, wherein the at least onepolysiloxane has the following structure (II) or (III):

wherein: m has a value of at least 1; m′ ranges from 0 to 75; n rangesfrom 0 to 75; n′ ranges from 0 to 75; each R, which may be identical ordifferent, is selected from H, OH, a monovalent hydrocarbon group, amonovalent siloxane group, and mixtures of any of the foregoing; and—R^(a) comprises the following structure (IV):

—R³—X  (IV)

wherein —R³ is selected from an alkylene group, an oxyalkylene group, analkylene aryl group, an alkenylene group, an oxyalkenylene group, and analkenylene aryl group; and X represents a group which comprises at leastone reactive functional group selected from a hydroxyl group, a carboxylgroup, an isocyanate group, a blocked polyisocyanate group, a primaryamine group, a secondary amine group, an amide group, a carbamate group,a urea group, a urethane group, a vinyl group, an unsaturated estergroup such as an acrylate group and a methacrylate group, a maleimidegroup, a fumarate group, an onium salt group such as a sulfonium groupand an ammonium group, an anhydride group, a hydroxy alkylamide group,and an epoxy group.

As used herein, “alkylene” refers to an acyclic or cyclic, saturatedhydrocarbon group having a carbon chain length of from C₂ to C₂₅.Nonlimiting examples of suitable alkylene groups include, but are notlimited to, those derived from propenyl, 1-butenyl, 1-pentenyl,1-decenyl, and 1-heneicosenyl, such as, for example (CH₂)₃, (CH₂)₄,(CH₂)₅, (CH₂)₁₀, and (CH₂)₂₃, respectively, as well as isoprene andmyrcene.

As used herein, “oxyalkylene” refers to an alkylene group containing atleast one oxygen atom bonded to, and interposed between, two carbonatoms and having an alkylene carbon chain length of from C₂ to C₂₅.Nonlimiting examples of suitable oxyalkylene groups include thosederived from trimethylolpropane monoallyl ether, trimethylolpropanediallyl ether, pentaerythritol monoallyl ether, polyethoxylated allylalcohol, and polypropoxylated allyl alcohol, such as—(CH₂)₃OCH₂C(CH₂OH)₂(CH₂CH₂—).

As used herein, “alkylene aryl” refers to an acyclic alkylene groupsubstituted with at least one aryl group, for example, phenyl, andhaving an alkylene carbon chain length of C₂ to C₂₅. The aryl group canbe further substituted, if desired. Nonlimiting examples of suitablesubstituent groups for the aryl group include, but are not limited tohydroxyl groups, benzyl groups, carboxylic acid groups, and aliphatichydrocarbon groups. Nonlimiting examples of suitable alkylene arylgroups include, but are not limited to, those derived from styrene and3-isopropenyl-∝,∝-dimethylbenzyl isocyanate, such as —(CH₂)₂C₆H₄— and—CH₂CH(CH₃)C₆H₃(C(CH₃)₂(NCO). As used herein, “alkenylene” refers to anacyclic or cyclic hydrocarbon group having one or more double bonds andhaving an alkenylene carbon chain length of C₂ to C₂₅. Nonlimitingexamples of suitable alkenylene groups include those derived frompropargyl alcohol and acetylenic diols, for example,2,4,7,9-tetramethyl-5-decyne-4,7-diol that is commercially availablefrom Air Products and Chemicals, Inc, of Allentown, Pa. as SURFYNOL 104.

Formulae (II) and (III) are diagrammatic, and are not intended to implythat the parenthetical portions are necessarily blocks, although blocksmay be used where desired. In some cases the polysiloxane may comprise avariety of siloxane units. This is increasingly true as the number ofsiloxane units employed increases, and especially true when mixtures ofa number of different siloxane units are used. In those instances wherea plurality of siloxane units are used and it is desired to form blocks,oligomers can be formed which can be joined to form the block compound.By judicious choice of reactants, compounds having an alternatingstructure or blocks of alternating structure may be used.

The curable resinous binder is present in the composition in amounts of80 to 99, more typically 85 to 99 percent by weight. The inorganicparticles are present in the composition in amounts of 0.5 to 10, moretypically 0.5 to 5 percent by weight, and the surface active agent istypically present in the coating composition in amounts of 0.5 to 10,more typically 2 to 12.5 percent by weight. The above percentages byweight are based on total solids weight of the composition.

When the coating compositions are applied by electrodeposition, they arein the form of an aqueous dispersion.

The term “dispersion” is believed to be a two-phase transparent,translucent or opaque system in which the solids of the composition isin the dispersed phase and the water is in the continuous phase. Theaverage particle size of the solids phase is generally less than 1.0 andusually less than 0.5 microns, preferably less than 0.15 micron.

The concentration of the solids phase in the aqueous medium is at least1 and usually from about 2 to about 60 percent by weight based on totalweight of the aqueous dispersion.

The electrodeposition bath can be prepared by predispersing in water andoptional co-diluents the curable resinous composition that includes theionic film-forming resin and the crosslinking agent. Typically, theresin solids of this predispersion is about 60 to 80% by weight based ontotal weight of the dispersion. The dispersion can then be let down withadditional water and optional co-diluent to form the electrodepositionbath. The inorganic particles and the surface active agent can be addedto the predispersion or to the electrodeposition bath itself.Preferably, the inorganic particles are prereacted with the surfaceactive agent and the prereacted material added to the resinouspredispersion. Prereaction does not necessarily mean an actual chemicalreaction between the inorganic particles and the surface active agent.It simply means that the two are mixed together followed by heatingtypically from 50 to 150° C. for 10 to 60 minutes to form a mixturewhich may be an actual reaction product which has been found to be moreeasily incorporated into the coating composition.

When the compositions of the present invention are in the form ofelectrodeposition baths, the so/ids content of the electrodepositionbath are usually within the range of about 5 to 25 percent by weightbased on total weight of the electrodeposition bath.

As aforementioned, besides water, the aqueous medium may contain aco-diluent such as a coalescing solvent. Useful coalescing solventsinclude hydrocarbons, alcohols, esters, ethers and ketones. Thepreferred coalescing solvents include alcohols, polyols and ketones.Specific coalescing solvents include isopropanol, butanol,2-ethylhexanol, isophorone, 2-methoxypentanone, ethylene and propyleneglycol and the monoethyl, monobutyl and monohexyl ethers of ethyleneglycol. The amount of coalescing solvent is generally between about 0.01and 25 percent and when used, preferably from about 0.05 to about 5percent by weight based on total weight of the aqueous medium.

The coating compositions can also contain dyes or transparent pigmentsto tint the coating without substantially affecting the transparency ofthe coating.

When the aqueous dispersions as described above are employed for use inelectrodeposition, the aqueous dispersion is placed in contact with anelectrically conductive anode and an electrically conductive cathode,with the surface to be coated being the cathode in cationicelectrodeposition and the anode in anionic electrodeposition. Asaforementioned, in the method of the present invention, it is preferredthat the substrate serves as the cathode. Following contact with theaqueous dispersion, an adherent film of the coating composition isdeposited on the substrate that is serving as an electrode when asufficient voltage is impressed between the electrodes. The conditionsunder which electrodeposition is carried out are in general, similar tothose used in electrodeposition of other types of coatings. The appliedvoltage may be varied and can be, for example, as low as 1 volt to ashigh as several thousand volts, but typically between 50 and 500 volts.The current density is usually between 0.5 ampere and 5 amperes persquare foot and tends to decrease during electrodeposition indicatingthe formation of an insulating film.

When the compositions are cured, the inorganic particles migrate to thesurface region of the cured composition such that the concentration inthe surface region is greater than in the bulk region of the curedcomposition.

As used herein “surface region” of the cured composition means theregion which is generally parallel to the exposed air-surface of thecoated substrate and which has thickness generally extendingperpendicularly from the surface of the cured coating to a depth rangingfrom at least 20 nanometers to 150 nanometers beneath the exposedsurface. In certain embodiments, this thickness of the surface regionranges from at least 20 nanometers to 100 nanometers, and can range fromat least 20 nanometers to 50 nanometers. As used herein, “bulk region”of the cured composition means the region which extends beneath thesurface region and which is generally parallel to the surface of thecoated substrate. The bulk region has a thickness extending from itsinterface with the surface region through the cured coating to thesubstrate or coating layer beneath the cured composition.

The concentration of particles in the cured composition can becharacterized in a variety of ways. For example the average numberdensity of particles (i.e., the average number or population ofparticles per unit volume) in the surface region is greater than theaverage number density in the bulk region. Alternatively, the averagevolume fraction (i.e., volume occupied by particles/total volume) oraverage weight percent per unit volume, i.e., ((the weight of particleswithin a unit volume of cured coating)/(total weight of the unit volumeof cured coating))×100% of the particles in the surface region isgreater than the average volume fraction or average weight percent ofparticles within the bulk region.

The concentration of particles (as characterized above) present in thesurface region of the cured coating can be determined, if desired, by avariety of surface analysis techniques well known in the art, such asTransmission Electron Microscopy (“TEM”), Surface Scanning ElectronMicroscopy (“X-SEM”), Atomic Force Microscopy (“AFM”), and X-rayPhotoelectron Spectroscopy.

For example the concentration of particles present in the surface regionof the cured coating may be determined by cross-sectional transmissionelectron microscopy techniques. A useful transmission electronmicroscopy method is described generally as follows. A coatingcomposition is applied to a substrate and cured. Samples of the curedcoating are then removed or delaminated from the substrate and embeddedin a cured epoxy resin using techniques as are well known in the art.The embedded samples then can be microtomed at room temperature usingtechniques well known in the art, such as by forming a block face. Thesections can be cut using a 45° diamond knife edge mounted in a holderwith a “boat cavity” to hold water. During the cutting process, sectionsfloat to the surface of the water in the boat cavity. Once a few cutsreach an interference color of bright to dark gold (i.e., approximately100 to 150 nanometers thickness), individual samples typically arecollected onto a formvar-carbon coated grid and dried at ambienttemperature on a glass slide. The samples are then placed in a suitabletransmission electron microscope, such as a Philips CM12 TEM, andexamined at various magnifications, such as at 105,000× magnification,for documentation of particle concentration at the surface region, viaelectron micrography. The concentration of particles in a surface regionof a cured coating can be ascertained upon visual inspection of theelectron micrograph.

The coatings formed from the cured compositions according to the presentinvention can have outstanding initial scratch (mar) resistanceproperties, as well as post-weathering or “retained” scratch (mar)resistance, which can be evaluated by measuring the gloss of coatedsubstrates before and after abrading of the coated substrates.

The initial 20° gloss of a coated substrate according to the presentinvention can be measured with a 20° NOVO-GLOSS 20 statisticalglossmeter, available from Gardner Instrument Company, Inc. The coatedsubstrate can be subjected to scratch testing by linearly scratching thecoating or substrate with a weighted abrasive paper for ten double rubsusing an Atlas AATCC Scratch Tester, Model CM-5, available from AtlasElectrical Devices Company of Chicago, Ill. The abrasive paper is 3M281Q WETORDRY™ PRODUCTION™ 9 micron polishing paper sheets, which arecommercially available from 3M Company of St. Paul, Minn. Panels arethen rinsed with tap water and carefully patted dry with a paper towel.The 20° gloss is measured on the scratched area of each test panel. Thenumber reported is the percent of the initial gloss retained afterscratch testing, i.e., 100%× scratched gloss I initial gloss. Since the20° gloss of a bright reflective coated substrate is somewhatmeaningless, the 20° gloss is determined over a black substrate to whichthe coating compositions of the invention have been applied. Forexample, the substrate can be first coated with a coating compositioncontaining an electroconductive black pigment such as carbon blackfollowed by electrodeposition of the coating composition of theinvention. When tested in this manner, the cured compositions have aninitial gloss (as measured using a 20° NOVO-GLOSS 20 statisticalglossmeter, available from Gardner Instrument Company) of greater than70 and retain at least 70% of their initial gloss after abrasiontesting.

In addition, the cured coatings have a retained scratch resistance (asmeasured using the scratch test method described above after theunscratched test panels were subjected to simulated weathering by QUVexposure to UVA-340 bulbs in a weathering cabinet available from Q PanelCompany) such that greater than 50 percent of initial 20° gloss isretained after weathering.

Illustrating the invention are the following examples, which, however,are not to be considered as limiting the invention to their details.Unless otherwise indicated, all parts and percentages in the followingexamples, as well as throughout the specification, are by weight.

EXAMPLES Example A Polysiloxane

This example describes the preparation of polysiloxane polyol, a productof the hydrosilylation of polysiloxane with an approximate degree ofpolymerization of 3 to 4, i.e. (Si—O)₃ to (Si—O)₄. The polysiloxanepolyol was prepared as follows:

To a suitable reaction vessel equipped with a means for maintaining anitrogen blanket, was added 1032.0 kg of trimethylolpropane monoallylether and 84.4 g of anhydrous sodium acetate. The mixture was spargedwith nitrogen for 20 minutes with stirring at room temperature, and asolution of chloroplatinic acid (29.1 g in 570.0 g of isopropanol) wasadded, followed by 952.5 g of toluene. The mixture was heated to 80° C.,and 680.4 kg of MASILWAX BASE 135 (polysiloxane containing siliconhydride, available from Emerald Performance Materials) was added over 5hours and 30 minutes. The temperature was maintained at 80° C. until thesilicon hydride peak at 2150 cm⁻¹ in the infrared spectrum was no longerobservable.

Example B Silica Dispersion

This Example describes a colloidal silica dispersion prepared asfollows:

A suitable reaction vessel equipped for vacuum distillation was flushedwith N₂. To the reaction flask was added 236.3 g of the polysiloxanepolyol of Example A, 337.2 g of ORGANOSILICASOL MT-ST (colloidal silicaavailable from Nissan Chemicals), and 129.4 g of methyl amyl ketone. Theresulting mixture was vacuum distilled at 25° C. until 212.1 g ofsolvent had been removed. The mixture was heated to 40° C. for 2 hours,and then to 60° C. for an additional 2 hours. To the reaction flask wasadded 90.2 g of 4-methylhexahydrophthalic anhydride over 30 minutes.After completion of this addition, the mixture was heated to 90° C. Whenthe anhydride peak at 1790 cm⁻¹ in the infrared spectrum was no longerobservable, 175.9 g of CARDURA E-10 (neodecanoic acid glycidyl ester)was added over 2 hours. After the first 10 minutes of the addition, 0.75g of benzyldimethylamine was added to the reaction vessel. The reactiontemperature was maintained at 90° C. for about 16 hours, and then 13.56g of CARDURA E-10 was added. After about 20 hours at 90° C. a final acidvalue of 11.5 was reached.

Example I

The colloidal silica dispersion of Example B was used to modify acationic electrodepositable clear coating composition available from PPGindustries as ELECTROCLEAR 2700. The amino group-containing acrylicpolymer and aminoplast curing agent were mixed with the silicadispersion of Example B. Lactic acid was added to the mixture topartially neutralize the amino group-containing acrylic polymer (70% TN)and the mixture dispersed in water to a 30% solids content. For use inan electrodeposition bath, the dispersions were further thinned withwater to a solids content of fifteen (15) percent by weight.

Reference is made to the FIGURE, where it can be seen that theconcentration of colloidal silica particles is greater at the surface 2of the cured coating than in the bulk region. In other words, theconcentration of the colloidal silica particles in the region extendingfrom the exposed air-surface interface to a depth of 20 to 50 nanometersis greater than the concentration of the silica particles in the bulkregion of the coating 3.

Example II (Control)

For the purposes of control, unmodified ELECTROCLEAR 2700 was comparedto Example I.

Cationic electrodeposition baths of Examples and it were prepared. Thebaths had solids content of 15% by weight and bath conductivities of700-900 microohms per centimeter at 27° C. Aluminum panels wereelectrodeposited in the baths at 130-250 volts for 30-90 seconds at abath temperature of 26-32° C. Smooth continuous films were obtained. Thefilms were cured at 177° C. for 30 minutes to produce tack-free coatingswith good appearance.

Test Procedures:

Scratch resistance of the coated test panels was measured using thefollowing method: Initial 20° gloss of the coated panels is measuredwith a 20° NOVO-GLOSS 20 statistical glossmeter, available from GardnerInstrument Company, Inc. Coated panels were subjected to scratch testingby linearly scratching the coated surface with a weighted abrasive paperfor ten double rubs using an Atlas AATCC Scratch Tester, Model CM-5,available from Atlas Electrical Devices Company of Chicago, Ill. Theabrasive paper is 3M 2819 WET OR DRY PRODUCTION 9 micron polishing papersheets available from the 3M Company. Panels were then rinsed with waterand carefully patted dry. The 20° gloss was measured on the scratchedarea of each test panel. The number reported is the percent of theinitial gloss retained after scratch testing, i.e., 100%× scratchedgloss/initial gloss. Post-weathering scratch resistance (retainedscratch resistance) was measured using the scratch test method describedabove after the unscratched test panels were subjected to simulatedweathering by QUV exposure to UVA-340 bulbs in a weathering cabinetavailable by Q Panel Co. Testing was as follows: a cycle of 70° C. for 8hours followed by 50° C. for 4 hours (total exposure time of 100 hours).The number reported is the percent of the initial gloss retained afterretained scratch testing, i.e., 100× retained scratched gloss I initialgloss. The results are reported in Table 1 below.

TABLE 1 % Initial 20° % Initial 20° Gloss After Gloss Retained 20° GlossMar/Scratch Post-weathering Example (Initial) Test Mar/Scratch Test I(Control) 887 57.7% 36.9% II 912 82.8% 61.7%

The results reported in Table 1 above illustrate that, compared with thecontrol, the electrocoating multi-component compositions of theinvention of Example II provide coatings with better initial andretained scratch resistance after simulated weathering testing.

1. A coated article comprising: (a) a decorative metal substrate havinga specular gloss greater than 400, with the proviso that the decorativemetal substrate is not a pigmented coating, (b) a transparent curedcoating thereon containing a resinous binder, 0.5 to 10 percent byweight based on total solids weight of the coating of a surface activeagent and inorganic particles in which the concentration of particles inthe exposed surface region of the cured coating is greater than the bulkregion of the cured coating.
 2. The coated article of claim 1 in whichthe decorative metal is selected from the group consisting of brass,bronze, and aluminum and precious metals.
 3. The coated article of claim1 in which the decorative metal is selected from the group consisting ofhardware, aluminum and trim parts and jewelry.
 4. The coated article ofclaim 1 in which the transparent cured coating is applied byelectrodeposition.
 5. The coated article of claim 4 in which theelectrodeposition is cationic electrodeposition.
 6. The coated articleof claim in which the cured coating is derived from a (meth)acrylicresin.
 7. The coated article of claim 1 in which the inorganic particleshave a particle size less than 1000 nanometers.
 8. The coated article ofclaim 1 in which the inorganic particles have a Mohs' hardness greaterthan
 5. 9. The coated article of claim 1 in which the inorganicparticles are colloidal silica.
 10. The coated article of claim 1 inwhich the particles are present in the cured coating composition inamounts of 0.5 to 10 percent by weight based on weight of the curedcoating.
 11. The coated article of claim 1 in which the surface activeagent is a polysiloxane.